The present invention relates to an electric metal sheet for an electric machine, the main body of which is an individual sheet made of a magnetizable material, the individual sheet having a plurality of cut-outs. Furthermore, the present invention relates to a method for producing an electric metal sheet for an electric machine by punching out an individual sheet made of a magnetizable sheet blank, the individual sheet having a plurality of cut-outs. The expression “electric metal sheet” is used here not as a material name but as a designation for a single, ready formed metal sheet which is typically stacked together with identical sheets to form a sheet stack for an electric machine.
An electric machine is herein understood to be a motor, a generator or alternatively a transformer. In particular, electric metal sheets are also used for the rotors of motors and generators of the aforementioned type.
For the greatest possible torque yield, the rotor metal sheets are dimensioned so that a reactance is as small as possible in the direction of a q-axis. Usually therefore, many large-area punched holes are provided in the rotor metal sheet in the direction of the q-axis. However, this leads to a weakening of the mechanical stability so that the rotary speed suitability is limited. Through the use of webs, the rotor metal sheet is stabilized against centrifugal forces. However, these webs lead to leakage flux, so that the efficiency of the electric machine is reduced.
A rotor metal sheet as shown in FIG. 1 is typically produced by a punching technique. An individual sheet is punched out from a sheet blank. Such individual sheets for a rotor are round and are assembled to a sheet stack which then has the desired magnetic properties of the rotor.
According to the example of FIG. 1, each individual sheet has punched holes 1 for guiding the magnetic field. Flux guidance areas 2 are produced between the punched holes 1. In order to increase the stability of the individual sheet and also of the whole rotor, provided in the cut-outs is a plurality of webs 3 which bridge the cut-outs and lead from a flux guidance area 2 to an adjacent flux guidance area 2. Since the cut-outs 1 are to extend, for magnetic reasons, to the edge of the individual sheet although, for stability reasons, this is not suitable, the individual cut-outs 1 are bridged at the outer periphery of the individual sheet by means of outer webs 4, so that the individual sheet is closed at the periphery. However, the many webs 3 and 4 lead to the aforementioned leakage flux and the resulting efficiency reduction.
The publication EP 2 768 117 A1 discloses a rotor of a reluctance machine with alternating magnetic and non-magnetic regions in the metal sheets. The non-magnetic regions are realized through non-magnetic structures that are provided by means of metallic integral bonding (rapid prototyping) in the intended portions of the metal sheets.
The document WO 2013/045142 A2 also discloses a method for producing a machine component for an electric machine. In order to prevent magnetic short-circuits, separating regions are provided which are created by applying a melting doping element along a region in the axial direction and by subsequent melting of the separating region.
Furthermore, the document JP 2002095227 A discloses a reluctance motor with a mechanically strengthened rotor. Non-magnetic members are integrated into cut-outs of the electric metal sheets.
In addition, the document EP 1 130 746 A1 discloses a rotor with flux barriers for a reluctance motor. In extension of cut-outs, non-magnetic portions are arranged on the outer periphery of each metal sheet.
The object of the present invention therefore lies in providing an electric metal sheet for an electric machine which has increased magnetic efficiency together with high stability. Furthermore, a corresponding production method is to be provided.